Optical transparent member and optical system using the same

ABSTRACT

It is an object to provide an optical transparent member capable of maintaining a high-performance antireflection effect for a base over a long period of time, and an optical system using the same, specifically an optical transparent member including on a base a layer containing SiO 2  as a main component, a layer containing Al 2 O 3  as a main component, and a plate crystal layer formed from plate crystals containing Al 2 O 3  as a main component, wherein the surface of the plate crystal layer has a shape of irregularities, and an optical system using the same.

This application is a division of U.S. patent application Ser. No.11/355,970, filed Feb. 17, 2006, now U.S. Pat. No. 7,811,684.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an optical transparent member having anantireflection performance and an optical system using the same, andmore particularly to an optical transparent member suitable forobtaining a high antireflection performance from a visible region to anear infrared region over a long period of time, and an optical systemusing the same.

Particularly, the optical transparent member of the present inventioncan adapt to a transparent base having any refractive index, shows anexcellent antireflection effect to visible light, and has a long-termweathering resistance, and therefore it can be used for optical membersof various kinds of displays of word processors, computers, televisions,plasma display panels and the like; polarizing plates of liquid crystalapparatuses; sunglass lenses, graduated eyeglass lenses, finder lensesfor cameras, prisms, fly-eye lenses, toric lenses, and various kinds ofoptical filters and sensors and the like consisting of various kinds ofoptical glass materials and transparent plastics; and further, opticalmembers of various kinds of optical lenses of image pickup opticalsystems using those optical members, observation optical systems such asbinoculars, projection optical systems for use in liquid crystalprojectors, scan optical systems for use in laser printers and the like,covers of various kinds of instruments, and window glasses ofautomobiles, electric trains and the like.

2. Related Background Art

It is known that an antireflection structure using a fine periodicstructure having a wavelength of the visible light region or a shorterwavelength forms a fine periodic structure having an appropriate pitchand height, and thereby shows an excellent antireflection performance ina wide wavelength region. As a method for forming a finely periodicstructure, coating of a film in which fine particles having a particlediameter equal to or less than the wavelength are dispersed (JapanesePatent No. 03135944) or the like is known.

It is known that a method of forming a fine periodic structure byformation of a pattern by a fine processing apparatus (electron beamlithography apparatus, laser interference light exposure apparatus,semiconductor light exposure apparatus, etching apparatus, etc.) allowsa pitch and a height to be controlled, and makes it possible to form afine periodic structure having an excellent antireflection property(Japanese Patent Application Laid-Open No. S50-70040).

As methods other than the methods described above, methods of growingboehmite that is an oxide hydroxide of aluminum on a base to obtain anantireflection effect are known. In these methods, a layer of aluminum(alumina) formed by the vacuum film formation process (Japanese PatentPublication No. S61-48124) or the liquid phase process (sol-gel process)(Japanese Patent Application Laid-Open No. H9-202649) is subjected to awater vapor treatment or a hot water dipping treatment to form a surfacelayer into boehmite to form a fine periodic structure, and thereby anantireflection film is obtained.

However, in a technique using fine particles, it is difficult to controlthe pitch and height of the fine periodic structure, and if a height forobtaining a sufficient antireflection effect is to be obtained, thepitch increases to cause scattering, and conversely, the lighttransmittance decreases.

The method of forming fine patterns by the fine processing apparatus hasa disadvantage that not only such a method of forming a pattern requiresvery large-scale equipment, thus requiring a very high capitalexpenditure, but also although the method is suitable for formation of apattern on a flat surface, it is very difficult to form a pattern on acomplicated shape such as a curved surface. In addition, the method isunsuitable for application to general-purpose optical elements becausethroughput is low and processing on a large area is difficult.

The method of growing boehmite on a base is convenient and has a highproductivity, but alumina and boehmite are amphoteric compounds and thusare easily decomposed by acids and alkalis. Consequently, when alkaliions and the like of the base migrate to the surface and the surface isbrought into an alkali atmosphere due to an exchange reaction with waterin air, maintenance of a shape of irregularities becomes difficult dueto decomposition of the surface and thus the performance is degraded.For a base having a refractive index significantly different from thatof alumina, a difference in refractive index at an interface between thebase and alumina is so large that the antireflection performance is notsufficiently exhibited.

SUMMARY OF THE INVENTION

The present invention has been made in view of the related art describedabove, and its object is to provide an optical transparent member whichcan maintain a high-performance antireflection effect over a long periodof time for any base, and an optical system using the same.

The present invention provides an optical transparent member configuredin a manner described below for achieving the above-mentioned object.

Namely, the present invention provides an optical transparent memberhaving on a base a layer containing SiO₂ as a main component, a layercontaining Al₂O₃ as a main component, and a plate crystal layer formedfrom plate crystals containing Al₂O₃ as a main component, wherein thesurface of the plate crystal layer consists of a shape ofirregularities.

It is preferable that on the base, the layer containing SiO₂ as a maincomponent, the layer containing Al₂O₃ as a main component, and the platecrystal layer formed from plate crystals containing Al₂O₃ as a maincomponent are stacked in this order.

It is preferable that the plate crystals of the plate crystal layercontaining Al₂O₃ as a main component are arranged in a direction of 45°or more and 90° or less with respect to the layer containing Al₂O₃ as amain component.

It is preferable that the thickness of the shape of irregularities ofthe surface of the plate crystal layer is 20 nm or more and 1000 nm orless.

It is preferable that for the shape of irregularities of the surface ofthe plate crystal layer, an average surface roughness Ra′ value obtainedby two-dimensional extension of a center line average roughness of thesurface with irregularities is 5 nm or more and 100 nm or less, and asurface area ratio S_(r)=S/S₀ (where S₀ represents the area when ameasurement surface is ideally flat and S represents the surface area ofan actual measurement surface) is 1.1 or more and 3.5 or less.

It is preferable that a refractive index n_(b) of the base, a refractiveindex n_(s) of the layer containing SiO₂ as a main component, and arefractive index n_(a) of the layer containing Al₂O₃ as a main componentmeet the relation of n_(b)≧n_(s)≧n_(a).

It is preferable that the thickness of the layer containing SiO₂ as amain component is 5 nm or more and 100 nm or less, and the thickness ofthe layer containing Al₂O₃ as a main component is 10 nm or more and 120nm or less.

In addition, the present invention provides an optical system having theabove-mentioned optical transparent member.

It is preferable that the optical system is an image pickup opticalsystem, an observation optical system, a projection optical system or ascan optical system.

The optical transparent member of the present invention has a layercontaining SiO₂ as a main component provided on a base and under a layercontaining Al₂O₃ as a main component, and the refractive index n_(b) ofthe base, the refractive index n_(s) of the layer containing SiO₂ as amain component, and the refractive index n_(a) of the layer containingAl₂O₃ as a main component meet the relation of n_(b)≧n_(s)≧n_(a), thusmaking it possible to further improve a low reflection property of theplate crystal layer formed from plate crystals containing alumina as amain component.

Moreover, the layer containing SiO₂ as a main component inhibitsmigration of an alkali component and the like from the base to thesurface, and can maintain an antireflection performance over a longperiod of time.

The optical member of the present invention has the surface of a basecoated with a layer containing SiO₂ as a main component, a layercontaining Al₂O₃ as a main component, and a plate crystal layer formedfrom plate crystals containing Al₂O₃ as a main component, in this order,and the outermost surface of the plate crystal layer has a shape ofirregularities. The plate crystal layer formed from plate crystals formsa shape of irregularities due to arrangement in a direction of 45° ormore and 90° or less with respect to the layer containing Al₂O₃ as amain component, the interval between plate surfaces in the layer,disorderliness of the orientation of the plate surface anddisorderliness of the size of plate crystals, and the thickness of thelayer is 20 nm or more and 1000 nm or less. For the density of the platecrystals, an average surface roughness value Ra′ obtained bytwo-dimensional extension of a center line average roughness of thecoating is 5 nm or greater, and a surface area ratio S_(r)=S/S₀ (whereS₀ represents the surface area when a measurement surface is ideallyflat and S represents the surface area of an actual measurement surface)is 1.1 or greater. The thickness of the layer having arranged platecrystals is 20 nm or more and 1000 nm or less.

The refractive index n_(b) of the base, the refractive index n_(s) ofthe layer containing SiO₂ as a main component, and the refractive indexn_(a) of the layer containing Al₂O₃ as a main component meet therelation of n_(b)≧n_(s)≧n_(a), the thickness of the layer containingSiO₂ as a main component is 5 nm or more and 100 nm or less, and thethickness of the layer containing Al₂O₃ as a main component is 10 nm ormore and 120 nm or less, whereby the refractive index is graduallyreduced from the base to the shape of irregularities of the surface ofthe plate crystal layer formed from plate crystals, and theantireflection effect of the plate crystal layer is significantlyimproved.

The layer containing SiO₂ as a main component isolates the basecontaining various components and the layer having a high reactivity andcontaining Al₂O₃ as a main component from each other, and inhibitsmigration of a reactive components such as alkalis from the base to thelayer containing Al₂O₃ as a main component is inhibited, thus making itpossible to stably exhibit an antireflection effect over a long periodof time.

As described above, the optical transparent member of the presentinvention can stably exhibit a high antireflection effect over a longperiod of time.

Other features and advantages of the present invention will be apparentfrom the following description taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram showing one embodiment of an opticaltransparent member of the present invention;

FIG. 2 is a photograph (scaling factor: ×100000) showing a result ofobservation of a layer formed on a glass substrate and having fineirregularities on the surface from the top surface by an FE-SEM inExample 1;

FIG. 3 is a photograph (scaling factor: ×150000) showing a result ofobservation of the cross-section of a layer formed on a glass substrateand having fine irregularities by an FE-SEM in Example 1;

FIG. 4 is a front view of the Sixth Example of the present invention;

FIG. 5 is a sectional view of the Sixth Example of the presentinvention;

FIG. 6 is a front view of the Seventh Example of the present invention;

FIG. 7 is a sectional view of the Seventh Example of the presentinvention;

FIG. 8 is a front view of the Eighth Example of the present invention;

FIG. 9 is a sectional view of the Eighth Example of the presentinvention;

FIG. 10 is a front view of the Ninth Example of the present invention;

FIG. 11 is a sectional view of the Ninth Example of the presentinvention;

FIG. 12 is a sectional view of the Tenth Example of the presentinvention;

FIG. 13 is a sectional view of the Eleventh Example of the presentinvention;

FIG. 14 is a sectional view of the Twelfth Example of the presentinvention; and

FIG. 15 is a sectional view of the Thirteenth Example of the presentinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention will be described in detail below.

FIG. 1 is a schematic diagram showing one embodiment of an opticaltransparent member of the present invention. In FIG. 1, the opticaltransparent member of the present invention has on a base 21 a layer 22containing SiO₂ as a main component, a layer 23 containing Al₂O₃ as amain component, and a plate crystal layer 24 formed from plate crystalscontaining Al₂O₃ as a main component, and the surface of the platecrystal layer 24 has a shape of irregularities 25.

The plate crystals containing Al₂O₃ (alumina) as a main component areformed by using an oxide or a hydroxide of aluminum or a hydrate thereofas a main component. Especially preferable crystals are boehmite. Byplacing these plate crystals, their end portions form fineirregularities, and therefore it is preferable that the plate crystalsare selectively arranged in a direction of 45° or more and 90° or lesswith respect to the surface of a layer for increasing the height of thefine irregularities and reducing the intervals therebetween.

The thickness of the crystal layer formed from plate crystals ispreferably 20 nm or more and 1000 nm or less, more preferably 50 nm ormore and 1000 nm or less. If the thickness of the layer forming theirregularities is 20 nm or more and 1000 nm or less, an antireflectionperformance by a structure of fine irregularities is effective, thepossibility that the mechanical strength of the irregularities isimpaired is eliminated, and the structure of fine irregularities becomesadvantageous in terms of production costs. More preferably, thethickness is 50 nm or more and 1000 nm or less, whereby theantireflection performance is further improved.

The surface density of the fine irregularities of the present inventionis also important, and the corresponding average surface roughness Ra′value obtained by two-dimensional extension of a center line averageroughness is 5 nm or greater, more preferably 10 nm or greater, furtherpreferably 15 nm or more and 100 nm or less. The surface area ratioS_(r) is 1.1, more preferably 1.15 or greater, further preferably 1.2 ormore and 3.5 or less.

One of methods for evaluating an obtained structure of fineirregularities is observation of the surface of the structure of fineirregularities by a scanning probe microscope, and by the observation,the average surface roughness Ra′ value obtained by two-dimensionalextension of the center line average roughness Ra′ of a layer and thesurface area ratio S_(r) are determined. Namely, the average surfaceroughness Ra′ value (nm) is a value such that the center line averageroughness Ra′ defined in JIS B 0601 is applied to a measurement surfaceand three-dimensionally extended, and the Ra′ value is expressed as a“value obtained by averaging absolute values of deviations from areference surface to a specified surface” and given by the followingformula (1).

$\begin{matrix}{{Ra}^{\prime} = {\frac{1}{S_{0}}{\int_{Y_{B}}^{Y_{T}}{\int_{X_{L}}^{X_{R}}{{{{F\left( {X,Y} \right)} - Z_{0}}}{\mathbb{d}_{X}\mathbb{d}_{Y}}}}}}} & (1)\end{matrix}$

Ra′: average surface roughness value (nm),

S₀: area when the measurement surface is ideally flat,|X_(R)-X_(L)|×|Y_(T)-T_(B)|,

F(X, Y): height at a measurement point (X, Y), where X is an Xcoordinate and Y is a Y coordinate,

X_(L)-X_(R): range of X coordinates on the measurement surface,

Y_(B)-Y_(T): range of Y coordinates on the measurement surface,

Z₀: average height within the measurement surface.

The surface area ratio S_(r) is determined by S_(r)=S/S₀ (S₀: area whenthe measurement surface is ideally flat. S: surface area of an actualmeasurement surface). The surface area of an actual measurement surfaceis determined as follows. The measurement surface is divided into verysmall triangles consisting of closest three data points (A, B, C), andthen the area ΔS of each very small triangle is determined using avector product. ΔS (ΔABC) equals [s(s-AB)(s-BC)(s-AC)]^(0.5) (where AB,BC and AC are the lengths of the sides, and S≡0.5 (AB+BC+AC) holds), andthe total sum of the areas ΔS is a surface area S to be determined. IfRa′ as the surface density of the fine irregularities is 5 nm or greaterand S_(r) is 1.1 or greater, antireflection by the structure ofirregularities can be realized. If Ra′ is 10 nm or greater and S_(r) is1.15 or greater, the antireflection effect becomes higher than that ofthe former case. If Ra′ is 15 nm or greater and S_(r) is 1.2 or greater,the structure of irregularities has a performance capable of enduringpractical use. However, if Ra′ is 100 nm or greater and S_(r) is 3.5 orgreater, the effect of scattering by the structure of irregularitiespredominates over the antireflection effect so that a sufficientantireflection performance cannot be obtained.

The layer containing Al₂O₃ as a main component may be any amorphousoxide coating containing Al₂O₃ as a main component, and as a differentkind of component, an oxide such as TiO₂, ZrO₂, SiO₂, ZnO or MgO may beadded alone, or two or more of these oxides maybe selected, combined andadded. Specifically, the layer is selected so that the relation of therefractive index n_(a) of this film with the refractive index n_(s) ofthe layer containing SiO₂ as a main component is n_(s)≧n_(a) as a resultof controlling the contents of the components. In this case, apreferable mol % ratio to the film of Al₂O₃ is 50% or more and 100% orless, more preferably 70% or more and 100% or less. Consequently, therefractive index continuously decreases over a range from the base to aninterface with air, and along with the effect of the layer havingarranged plate crystals containing alumina as a main component, a highantireflection performance can be realized.

The layer of the present invention containing SiO₂ as a main componentmay be any amorphous oxide coating containing SiO₂ as a main component,and as a different kind of component, oxides such as TiO₂ and ZrO₂ maybe added alone or in combination. Specifically, the layer is selected sothat migration of an alkali and the like to the layer containing Al₂O₃as a main component can be inhibited and the relation of the refractiveindex n_(s) of this film with the refractive index n_(b) of the base isn_(b)≧n_(s) as a result of controlling the contents of the components.In this case, a preferable mol % ratio to the film of SiO₂ is 40% ormore and 100% or less, more preferably 60% or more and 100% or less.Consequently, the refractive index continuously decreases over a rangefrom the base to an interface with air, and along with the effects ofthe plate crystal layer formed from plate crystals containing Al₂O₃ as amain component and the layer containing Al₂O₃ as a main component, ahigh antireflection performance can be realized. Furthermore, by addingan acid component such as phosphoric acid in addition to theabove-mentioned oxides, the effect of inhibiting migration of an alkaliand the like from the base to the layer containing Al₂O₃ as a maincomponent can be improved.

The optical transparent member of the present invention can be formed bya publicly known gas phase process such as CVD or PVD, a liquid phaseprocess such as a sol-gel process, hydrothermal synthesis using aninorganic salt, or the like. By such an approach, plate crystalsconsisting of plate crystals containing alumina as a main component canbe provided directly after the layer containing SiO₂ as a main componentand the layer containing Al₂O₃ as a main component are formed in order.Alternatively, after forming a layer of metal Al alone or a metal layercontaining metal Al and any of metal Zn and metal Mg on the two layersof layers, the surface of the layer may be dissolved or precipitated byimmersion in hot water at 50° C. or higher or exposure to water vapor toprovide plate crystals of alumina. Alternatively, after forming a layerof Al₂O₃ alone or one or more oxide layer containing Al₂O₃ and any ofZrO₂, SiO₂, TiO₂, ZnO and MgO on the layer containing SiO₂ as a maincomponent, the surface of the layer may be selectively dissolved orprecipitated to provide plate crystals of alumina. Among them,preferable is a method in which a gel film formed by coating a sol-gelcoating solution containing SiO₂ and a sol-gel coating solutioncontaining Al₂O₃ in order is treated with hot water to grow aluminaplate crystals.

For a raw material of the gel film obtained from a sol-gel coatingsolution containing Al₂O₃, an Al compound is used, or at least one ofcompounds of Zr, Si, Ti, Zn and Mg is used together with the Alcompound. As raw materials of Al₂O₃, ZrO₂, SiO₂, TiO₂, ZnO and MgO,alkoxides of respective metals and salt compounds such as chlorides andnitrates may be used. Metal alkoxides are preferably used in terms offilm formability particularly for ZrO₂, SiO₂ and TiO₂ raw materials.

Aluminum compounds include, for example, aluminum ethoxide, aluminumisopropoxide, aluminum-n-butoxide, aluminum-sec-butoxide,aluminum-tert-butoxide, aluminum acetylacetate or oligomers of thesecompounds, aluminum nitrate, aluminum chloride, aluminum acetate,aluminum phosphate, aluminum sulfate and aluminum hydroxide.

Specific examples of zirconium alkoxides include zirconiumtetramethoxide, zirconium tetraethoxide, zirconium tetra n-propoxide,zirconium tetraisopropoxide, zirconium tetra n-butoxide and zirconiumtetra t-butoxide.

For the silicon alkoxide, various kinds of compounds expressed by thegeneral formula Si(OR)₄ may be used. R is a same or different loweralkyl group such as a methyl group, an ethyl group, a propyl group, anisopropyl group, a butyl group or an isobutyl group.

Titanium alkoxides include, for example, tetramethoxy titanium,tetraethoxy titanium, tetra n-propoxy titanium, tetraisopropoxytitanium, tetra n-butoxy titanium and tetraisobutoxy titanium.

Zinc compounds include, for example, zinc acetate, zinc chloride, zincnitrate, zinc stearate, zinc oleate and zinc salicylate, and especiallypreferable are zinc acetate and zinc chloride.

Magnesium compounds include magnesium alkoxides such as dimethoxymagnesium, diethoxy magnesium, dipropoxy magnesium and dibutoxymagnesium, magnesium acetylacetate and magnesium chloride.

Organic solvents, which may be any organic solvents which do not causeraw materials such as the above-mentioned alkoxides to gelate, include,for example, alcohols such as methanol, ethanol, 2-propanol, butanol,ethylene glycol or ethylene glycol-mono-n-propyl ether; various kinds ofaliphatic or alicyclic hydrocarbons such as n-hexane, n-octane,cyclohexane, cyclopentane and cyclooctane; various kinds of aromatichydrocarbons such as toluene, xylene and ethyl benzene; various kinds ofesters such as ethyl formate, ethyl acetate, n-butyl acetate, ethyleneglycol monomethyl ether acetate, ethylene glycol monoethyl ether acetateand ethylene glycol monobuthyl ether acetate; various kinds of ketonessuch as acetone, methyl ethyl ketone, methyl isobutyl ketone andcyclohexanone; various kinds of ethers such as dimethoxy ethane,tetrahydrofuran, dioxane and diisopropyl ether; various kinds ofchlorinated hydrocarbons such as chloroform, methylene chloride, carbontetrachloride and tetrachloroethane; and aprotic polar solvents such asN-methylpyrolidone, dimethyl formamide, dimethyl acetamide and ethylenecarbonate. Among various kinds of solvents described above, alcohols arepreferably used in terms of stability of a solution.

If an alkoxide raw material is used, particularly alkoxides of aluminum,zirconium and titanium are highly reactive to water, and are abruptlyhydrolyzed by addition of moisture in air or water, resulting in opacityand precipitation. Aluminum chloride compounds, zinc chloride compoundsand magnesium chloride compounds are hard to be dissolved in an organicsolvent alone, and the stability of their solutions is low. Forprevention of such a situation, a stabilizer is preferably added tostabilize the solution.

Stabilizers may include, for example, β-diketone compounds such asacetyl acetone, dipyrobilemethane, trifluoroacetylacetone,hexafluoroacetylacetone, benzoylacetone and dibenzoylmethane;β-ketoester compounds such as methyl acetoacetate, ethyl acetoacetate,allyl ketoacetate, benzyl acetoacetate, acetoacetate-iso-propyl,acetoacetate-tert-butyl, acetoacetate-iso-butyl,acetoacetate-2-methoxyethyl and 3-keto-n-methyl valeriate; and alkanolamines such as monoethanol amine, diethanol amine and triethanol amine.The amount of stabilizer added is preferably 1 in terms of a molar ratioto the alkoxide or salt compound. After the stabilizer is added, acatalyst is preferably added for the purpose of promoting part of areaction in order to form an appropriate precursor. Catalysts mayinclude, for example, nitric acid, hydrochloric acid, sulfuric acid,phosphoric acid, acetic acid and ammonia.

For a raw material of the gel film obtained from a sol-gel coatingsolution containing SiO₂, a Si compound is used, or at least one ofcompounds of Ti and Zr is used together with the Si compound. As rawmaterials of SiO₂, TiO₂ and ZrO₂, alkoxides of respective metals andsalt compounds such as chlorides and nitrates may be used, but metalalkoxides are preferably used in terms of film formability. For themetal alkoxide, the solvent, the stabilizer and the like, theaforementioned compounds may be used. As a catalyst promoting part of areaction, an acid such as phosphoric acid is preferably used fortrapping an alkali migrating in the film. The composition ratio of eachcomponent is appropriately selected using SiO₂ (n=1.45 by itself), TiO₂(n=2.20 by itself) and ZrO₂ (n=1.90 by itself) so that the relation ofthe refractive index n_(s) with the refractive index n_(b) of the baseand the refractive index n_(a) of the layer containing Al₂O₃ as a maincomponent is n_(b)≧n_(s)≧n_(a). It is known that TiO₂ has a highrefractive index and increases a control range of the refractive indexof the film, while TiO₂ is caused to change from a non-crystal to ananatase crystal by a treatment of immersion in hot water or exposure towater vapor. In view of maintenance of homogeneity of a coating and theeffect of inhibition of migration of an alkali and the like, thefraction of TiO₂ in the film is preferably reduced to inhibitcrystallization into anatase, and the mol % ratio of TiO₂ in the film ispreferably less than 40%. It is more preferably 30% or less.

As a method for forming a layer using the above-described sol-gelcoating solution, for example, a know coating method such as a dippingmethod, a spin coating method, a spray method, a printing method, a flowcoating method and a combination thereof may be appropriately employed.The film thickness can be controlled by changing a lifting speed in thedipping method, a substrate rotation speed in the spin coating method,or the like, and changing the concentration of a coating solution. Amongthem, the lifting speed in the dipping method may be appropriatelyselected according to a required film thickness, but it is preferablethat after immersion, the film is lifted at a gentle uniform speed of,for example, about 0.1 to 3.0 mm/second. After coating of the layer, itmay be dried at room temperature for about 30 minutes. The film can alsobe dried or thermally treated at a higher temperature, and the higherthe thermal treatment temperature, the more easily the film isdensificated. In the case of a gel film containing Al₂O₃ as a maincomponent, a structure of large irregularities can be formed byincreasing the thermal treatment temperature. In the case of a gel filmcontaining SiO₂ as a main component, a capability of inhibitingmigration of an alkali and the like can be improved by increasing thethermal treatment temperature.

Then, a gel film formed by coating a sol-gel coating solution containingSiO₂ and a sol-gel coating solution containing Al₂O₃ in order isimmersed in hot water, whereby plate crystals containing Al₂O₃ as a maincomponent is precipitated to form a shape of irregularities of theoutermost surface. By immersion in hot water, the surface layer of thegel film formed by coating the sol-gel coating solution containing Al₂O₃in order undergoes a peptization action or the like, and some componentsare eluted, but due to a difference in solubility in hot water betweenvarious kinds of hydroxides, plate crystals containing Al₂O₃ as a maincomponent are precipitated on the surface layer of the gel film, andgrow. The temperature of hot water is preferably 40° C. to 100° C. Thehot water treatment time is about 5 minutes to about 24 hours.

For the hot water treatment of a gel film with oxides such as TiO₂,ZrO₂, SiO₂, ZnO and MgO as different kinds of components added to thefilm containing Al₂O₃ as a main component, crystallization is carriedout using a difference in solubility in hot water between thecomponents, and therefore unlike the hot water treatment of the singlecomponent film of Al₂O₃, the size of plate crystals can be controlledover a wide range by changing the composition of inorganic components.As a result, the shape of irregularities formed by plate crystals can becontrolled over the wide range. Moreover, if ZnO is used as asubcomponent, coprecipitation with Al₂O₃ is possible, and therefore therefractive index can be controlled over a further wide range, thusmaking it possible to realize an excellent antireflection performance.

Thickness of the layer of the present invention containing SiO₂ as amain component is 5 nm or more and 100 nm or less, further preferably 5nm or more and 80 nm or less. If the thickness is less than 5 nm, asufficient effect against migration of an alkali cannot be obtained. Ifthe thickness is greater than 100 nm, contribution to the reflectionreducing effect is reduced due to interference and the like. Thethickness of the layer containing Al₂O₃ as a main component is 10 nm ormore and 120 nm or less, further preferably 10 nm or more and 100 nm orless. If the thickness is less than 10 nm, the adhesion property ofplate crystals is degraded, and the gradient of a difference inrefractive index between the layer containing SiO₂ as a main componentand the plate crystal layer becomes so large that the opticalperformance is impaired. If the thickness is greater than 120 nm,contribution to the reflection reducing effect is reduced due tointerference and the like.

Bases for use in the present invention include glass, resins, glassmirrors and mirrors made of resin. Typical examples of resin basesinclude films and molded products of thermoplastic resins such aspolyester, triacetyl cellulose, cellulose acetate, polyethyleneterephthalate, polypropylene, polystyrene, polycarbonate, polymethylmethacrylate, ABS resins, polyphenylene oxide, polyurethane,polyethylene and polyvinyl chloride; cross-linked films and cross-linkedmolded products obtained from various kinds of thermoset resins such asunsaturated polyester resins, phenol resins, cross-linked polyurethane,cross-linked acryl resins and cross-linked saturated polyester resins.Specific examples of glass may include no-alkali glass and aluminasilicate glass. Bases for use in the present invention, which may bemade of any materials capable of being formed into a shape appropriateto a use purpose ultimately, include flat plates, films and sheets, andmay have a two-dimensional or three-dimensional curved surface. Thethickness can be appropriately determined, and is generally 5 mm orless, but is not limited thereto.

The optical transparent member of the present invention may be furtherprovided with a layer for imparting various kinds of functions, inaddition to the layers described above. For example, a hard coat layermay be provided on the layer of plate crystals for improving thehardness of the film, or a water-repellent layer of fluoroalkyl silaneor alkyl silane may be provided for imparting a water repellency. Forthe purpose of preventing deposition of contaminants, or the like, alayer of a material having a refractive index lower than that of platecrystals containing Al₂O₃ as a main component, or a layer consisting ofan amphipathic compound may be provided. For improving the adhesionbetween the base and the layer containing SiO₂ as a main component, anadhesive layer or a primer layer may be used. The refractive index ofother layers provided between the base and the layer containing SiO₂ asa main component is preferably an intermediate value between therefractive index of the base and the refractive index of the layercontaining SiO₂ as a main component.

The present invention will be described specifically with examples.However, the present invention is not limited to such examples.Transparent films obtained with examples and comparative examples andhaving fine irregularities on the surface were evaluated by the methodsdescribed below.

(1) Observation of Shape of Coating

The surface of a surface layer of a coating was photographicallyobserved (acceleration voltage; 10.0 kV, scaling factor; 30000) using ascanning electron microscope (FE-SEM, S4500 manufactured by HitachiLtd.). An average surface roughness Ra′ value obtained bytwo-dimensional extension of the center line average roughness definedin JIS B 0601 and a surface area ratio Sr were determined using ascanning probe microscope (SPM, DFM mode, SPI3800 manufactured by SeikoElectronic Industries Co., Ltd.).

(2) Measurement of Transmittance

A transmittance was measured over a range from a visible region to anear-infrared region using an automatic optical element measuringapparatus (ART-25GD manufactured by JASCO). A disc glass plate was used.The angles of incidence of light in measurements of a transmittance anda reflectivity were 0° and 10°, respectively.

(3) Measurement of Film Refractive Index

Measurements were made over a range of wavelengths from 380 nm to 800 nmby Ellipsometer VASE manufactured by J.A. Woollam JAPAN Co., Inc.

Example 1

A clear float glass substrate (composition: soda lime silicate type,refractive index ng=1.52) having a size of about 100 mm×100 mm and athickness of about 2 mm was ultrasonically washed with isopropylalcohol, dried, and then used as a glass substrate for coating.

Tetraethoxy silane (TEOS) was dissolved in ethanol (EtOH), a 0.01 Maqueous phosphoric acid solution was added to the resultant solution asa catalyst, and then the resultant mixture was stirred for 6 hours. Themolar ratio of the components at this time is TEOS:EtOH:H₃PO₄ aq=1:40:2.Titanium n-butoxide (TBOT) was dissolved in ethanol, ethyl acetoacetate(EAcAc) was then added to the resultant solution as a stabilizer, andthe resultant mixture was stirred at room temperature for 3 hours. Themolar ratio of the components is TBOT:EtOH:EAcAc=1:20:1. A TiO₂ solsolution was added to the aforementioned SiO₂ sol solution so that amolar ratio of SiO₂:TiO₂=95:5 was obtained, and the resultant mixturewas stirred at room temperature for 2 hours, and then used as aSiO₂—TiO₂ coating solution. Then, the aforementioned coating glasssubstrate was immersed in this coating solution, a coating film wasformed on the surface of the glass substrate by the dipping method (at alifting speed of 0.5 mm/second, and at 20° C. and 56% R.H.). The glasssubstrate was dried, and then thermally treated by baking at 400° C. foran hour, and a transparent amorphous SiO₂/TiO₂ film was coated thereon.

The thickness and the refractive index of the obtained film weremeasured, and the result of the measurement showed that the thicknessd_(s) was d_(s)=20 nm and the refractive index was n_(s)=1.48.

Then, Al (O-sec-Bu)₃ was dissolved in IPA, EAcAc was added to theresultant solution as a stabilizer, and the resultant mixture wasstirred at room temperature for about 3 hours. Thereafter, 0.01 M[HClaq.] was added to the resultant solution, and the resultant mixture wasstirred at room temperature for about 3 hours to prepare an Al₂O₃ solsolution. Here, the molar ratio of the solution wasAl(O-sec-Bu)₃:IPA:EAcAc:HClaq.=1:20:1:1. The aforementioned coatingsubstrate was immersed in the coating solution, and then a coating filmwas formed on the surface of the glass substrate by the dipping method(at a lifting speed of 2 mm/second, and at 20° C. and 56% R.H.). Theglass substrate was dried, and then thermally treated by baking at 400°C. for an hour, and a transparent amorphous Al₂O₃ film was coatedthereon. Then, the glass substrate was immersed in hot water at 100° C.for 30 minutes, and then dried at 100° C. for 10 minutes.

The surface of the obtained film was observed by the FE-SEM to find astructure of fine irregularities in which plate crystals containingAl₂O₃ as a main component were tangled at random and in a complicatedmanner as shown in FIG. 2. The cross-section was observed by the FE-SEMto observe an image in which plate crystals containing Al₂O₃ as a maincomponent were arranged selectively in a direction vertical to thesurface of the layer as shown in FIG. 3. The undermost layer in FIG. 3is a glass cross-section of the substrate, the intermediate layer is alayer consisting of the layer containing SiO₂ as a main component andthe layer containing Al₂O₃ as a main component, and the uppermost layeris a plate crystal layer consisting of plate crystals. The surface wasmeasured by the SPM, and the result of the measurement showed that theaverage surface roughness Ra′ value (nm) was Ra′=28 nm and the surfacearea ratio S_(r) was S_(r)=1.9.

Then, for the obtained film, the film thickness and the refractive indexwere measured using ellipsometry. The thickness and the refractive indexof each film are shown in Table 1.

For this substrate, a high-temperature and high-humidity test at atemperature of 60° C. and a humidity of 90% was conducted as anaccelerated test for examination on durability of an opticalperformance, and the transmittance was measured at a start time, after250 hours and after 500 hours. The results thereof are shown in Table 1.

Example 2

An S-TIH53 glass substrate (manufactured by OHARA INC., refractive indexn=1.84) having a size of about 50 mm×50 mm and a thickness of about 1 mmwas ultrasonically washed with isopropyl alcohol, dried, and then usedas a glass substrate for coating.

A TiO₂ sol solution was added to the aforementioned SiO₂ sol solution sothat a molar ratio of SiO₂:TiO₂=7:3 was obtained, and the resultantmixture was stirred at room temperature for 2 hours, and then used as aSiO₂—TiO₂ coating solution as in Example 1. Then, the aforementionedcoating glass substrate was immersed in this coating solution, a coatingfilm was formed on the surface of the glass substrate by the dippingmethod (at a lifting speed of 0.5 mm/second, and at 20° C. and 56%R.H.). The glass substrate was dried, and then thermally treated bybaking at 400° C. for an hour, and a transparent amorphous SiO₂/TiO₂film was coated thereon. The thickness and the refractive index of theobtained film were measured, and the result of the measurement showedthat the thickness was 28 nm and the refractive index n_(s) was 1.67.

Then, the aforementioned coating substrate was immersed in the Al₂O₃coating solution as in Example 1, and then a coating film was formed onthe surface of the glass substrate by the dipping method (at a liftingspeed of 2 mm/second, and at 20° C. and 56% R.H.). The glass substratewas dried, and then thermally treated by baking at 400° C. for an hour,and a transparent amorphous Al₂O₃ film was coated thereon. Then, theglass substrate was immersed in hot water at 100° C. for 30 minutes, andthen dried at 100° C. for 10 minutes.

The surface of the obtained film was observed by the FE-SEM to find astructure of fine irregularities in which plate crystals containingAl₂O₃ as a main component were tangled at random and complicatedly as inExample 1. For observation of the cross-section by the FE-SEM, astructure almost same as that in Example 1 was observed. The result ofmeasurement by the SPM showed that the average surface roughness Ra′value (nm) was Ra′=27 nm and the surface area ratio S_(r) was S_(r)=1.9.

Then, for the obtained film, the film thickness and the refractive indexwere measured using ellipsometry. The thickness and the refractive indexof each film are shown in Table 1.

For this substrate, a high-temperature and high-humidity test at atemperature of 60° C. and a humidity of 90% was conducted, and thetransmittance was measured at a start time, after 250 hours and after500 hours. The results thereof are shown in Table 1.

Example 3

An S-TIH53 substrate (manufactured by OHARA INC., refractive indexn_(b)=1.84) same as that in Example 2 was used as a glass substrate forcoating.

SiO₂/TiO₂ (7/3) was coated, and then a transparent amorphous SiO₂/TiO₂film was formed in the same manner as in Example 2. The thickness andthe refractive index of the obtained film were measured, and the resultof the measurement showed that the thickness was 28 nm and therefractive index was n_(s)=1.67.

Aluminum-sec-butoxide [Al(O-sec-Bu)₃] was dissolved in 2-propanol [IPA],ethyl acetoacetate [EAcAc] was added to the resultant solution as astabilizer, and the resultant mixture was stirred at room temperaturefor about 3 hours to prepare an Al₂O₃ sol solution. Here, the molarratio of the solution was Al(O-sec-Bu)₃:IPA:EAcAc=1:20:1.Titanium-n-butoxide [Ti(O-n-Bu)₄] was also dissolved in IPA, EAcAc wasadded to the resultant solution, and the resultant mixture was stirredfor about 3 hours to prepare a TiO₂ sol solution. The molar ratio of thesolution was Ti(O-n-Bu)₄:IPA:EAcAc=1:20:1. This TiO₂ sol solution wasadded in the aforementioned Al₂O₃ sol solution so that a weight ratio ofAl₂O₃:TiO₂=8:2 was obtained, the resultant mixture was stirred for about30 minutes, 0.01 M[HCl_(aq.)] was then added to the mixture, and theresultant mixture was stirred at room temperature for about 3 hours. Inthis way, a coating solution being an Al₂O₃/TiO₂ sol was prepared. Here,the amount of HCl_(aq.) added was an amount twice as large as theamounts of Al(O-sec-Bu)₃ and Ti(O-n-Bu)₄ in terms of a molar ratio.

Then, the aforementioned coating substrate was immersed in theAl₂O₃/TiO₂ coating solution as in Example 1, and then a coating film wasformed on the surface of the glass substrate by the dipping method (at alifting speed of 1 mm/second, and at 20° C. and 56% R.H.). The glasssubstrate was dried, and then thermally treated by baking at 400° C. foran hour, and a transparent amorphous Al₂O₃/TiO₂ film was coated thereon.Then, the glass substrate was immersed in hot water at 100° C. for 30minutes, and then dried at 100° C. for 10 minutes.

The surface of the obtained film was observed by the FE-SEM to find astructure of fine irregularities in which plate crystals containingAl₂O₃ as a main component were tangled at random and complicatedly as inExample 1. For observation of the cross-section by the FE-SEM, astructure almost same as that in Example 1 was observed. The result ofmeasurement by the SPM showed that the average surface roughness Ra′value (nm) was Ra′=18 nm and the surface area ratio S_(r) was S_(r)=1.5.

Then, for the obtained film, the film thickness and the refractive indexwere measured using ellipsometry. The thickness and the refractive indexof each film are shown in Table 1.

For this substrate, a high-temperature and high-humidity test at atemperature of 60° C. and a humidity of 90% was conducted, and thetransmittance was measured at a start time, after 250 hours and after500 hours. The results thereof are shown in Table 1.

Example 4

An S-TIH53 substrate (manufactured by OHARA INC., refractive indexn_(b)=1.84) same as that in Example 2 was used as a glass substrate forcoating.

SiO₂/TiO₂ (7/3) was coated, and then a transparent amorphous SiO₂/TiO₂film was formed in the same manner as in Example 2. The thickness andthe refractive index of the obtained film were measured, and the resultof the measurement showed that the thickness was 28 nm and therefractive index was n_(s)=1.67.

Aluminum-sec-butoxide [Al(O-sec-Bu)₃] was dissolved in 2-propanol [IPA],ethyl acetoacetate [EAcAc] was added to the resultant solution as astabilizer, and the resultant mixture was stirred at room temperaturefor about 3 hours to prepare an Al₂O₃ sol solution. Here, the molarratio of the solution was Al(o-sec-Bu)₃:IPA:EAcAc=1:20:0.5. Zinc acetatedihydrate [Zn(CH₃COO)₂.2H₂O] was also dissolved in [IPA], monoethanolamine [MEA] was added to the resultant solution, and the resultantmixture was stirred for about 3 hours to prepare a ZnO solution. Themolar ratio of the solution was Zn(CH₃COO)₂.2H₂O:IPA:MEA=1:10:1. ThisZnO sol solution was added in the aforementioned Al₂O₃ sol solution sothat a weight ratio of Al₂O₃:ZnO=0.8:0.2 was obtained, and the resultantmixture was stirred for about 30 hours. In this way, a coating solutionbeing an Al₂O₃—ZnO sol was prepared.

Then, the aforementioned coating substrate was immersed in the Al₂O₃/ZnOcoating solution as in Example 1, and then a coating film was formed onthe surface of the glass substrate by the dipping method (at a liftingspeed of 2 mm/second, and at 20° C. and 56% R.H.). The glass substratewas dried, and then thermally treated by baking at 400° C. for an hour,and a transparent amorphous Al₂O₃/ZnO film was coated thereon. Then, theglass substrate was immersed in hot water at 100° C. for 30 minutes, andthen dried at 100° C. for 10 minutes.

The surface of the obtained film was observed by the FE-SEM to find astructure of fine irregularities in which plate crystals containingAl₂O₃ as a main component were tangled at random and complicatedly as inExample 1. For observation of the cross-section by the FE-SEM, astructure almost same as that in Example 1 was observed. The result ofmeasurement by the SPM showed that the average surface roughness Ra′value (nm) was Ra′=32 nm and the surface area ratio S_(r) was S_(r)=2.0.

Then, for the obtained film, the film thickness and the refractive indexwere measured using ellipsometry. The thickness and the refractive indexof each film are shown in Table 1.

For this substrate, a high-temperature and high-humidity test at atemperature of 60° C. and a humidity of 90% was conducted, and thetransmittance was measured at a start time, after 250 hours and after500 hours. The results thereof are shown in Table 1.

Example 5

An S-TIH1 glass substrate (manufactured by OHARA INC., refractive indexn_(b)=1.71) having a size of about 50 mm×50 mm and a thickness of about1 mm was used as a glass substrate for coating.

Zirconium n-butoxide (ZBOT) was dissolved in ethanol, ethyl acetoacetate(EAcAc) was then added to the resultant solution as a stabilizer, andthe resultant mixture was stirred at room temperature for 3 hours. Themolar ratio of the components was ZBOT:EtOH:EAcAc=1:20:1. As in Example1, a TiO₂ sol solution and then a ZrO₂ sol solution were added to a SiO₂sol solution so that a molar ratio of SiO₂:TiO₂:ZrO₂=7:1:2 was obtained,and the resultant mixture was stirred at room temperature for 2 hours,and then used as a SiO₂—TiO₂—ZrO₂ coating solution. Then, theaforementioned coating glass substrate was immersed in this coatingsolution, and a coating film was formed on the surface of the glasssubstrate by the dipping method (at a lifting speed of 0.5 mm/second,and at 20° C. and 56% R.H.). The glass substrate was dried, and thenthermally treated by baking at 400° C. for an hour, and a transparentamorphous SiO₂/TiO₂/ZrO₂ film was coated thereon. The thickness and therefractive index of the obtained film were measured, and the result ofthe measurement showed that the thickness was 25 nm and the refractiveindex was n_(s)=1.62.

Aluminum-sec-butoxide [Al(O-sec-Bu)₃] was dissolved in 2-propanol [IPA],ethyl acetoacetate [EAcAc] was added to the resultant solution as astabilizer, and the resultant mixture was stirred at room temperaturefor about 3 hours to prepare an Al₂O₃ sol solution. Here, the molarratio of the solution was Al(O-sec-Bu)₃:IPA:EAcAc=1:20:0.5. Zinc acetatedihydrate [Zn(CH₃COO)₂.2H₂O] was also dissolved in [IPA], monoethanolamine [MEA] was added to the resultant solution, and the resultantmixture was stirred for about 3 hours to prepare a ZnO solution. Themolar ratio of the solution was Zn(CH₃COO)₂.2H₂O:IPA:MEA=1:10:1. ThisZnO sol solution was added in the aforementioned Al₂O₃ sol solution sothat a weight ratio of Al₂O₃:ZnO=0.9:0.1 was obtained, and the resultantmixture was stirred for about 3 hours. In this way, a coating solutionbeing an Al₂O₃—ZnO sol was prepared.

Then, the aforementioned coating substrate was immersed in the Al₂O₃/ZnOcoating solution as in Example 1, and then a coating film was formed onthe surface of the glass substrate by the dipping method (at a liftingspeed of 1 mm/second, and at 20° C. and 56% R.H.). The glass substratewas dried, and then thermally treated by baking at 400° C. for an hour,and a transparent amorphous Al₂O₃/ZnO film was coated thereon. Then, theglass substrate was immersed in hot water at 100° C. for 30 minutes, andthen dried at 100° C. for 10 minutes.

The surface of the obtained film was observed by the FE-SEM to find astructure of fine irregularities in which plate crystals containingAl₂O₃ as a main component were tangled at random and in a complicatedmanner as in Example 1. For observation of the cross-section by theFE-SEM, a structure almost same as that in Example 1 was observed. Theresult of measurement by the SPM showed that the average surfaceroughness Ra′ value (nm) was Ra′=30 nm and the surface area ratio S_(r)was S_(r)=1.9.

Then, for the obtained film, the film thickness and the refractive indexwere measured using ellipsometry. The thickness and the refractive indexof each film are shown in Table 1.

For this substrate, a high-temperature and high-humidity test at atemperature of 60° C. and a humidity of 90% was conducted, and thetransmittance was measured at a start time, after 250 hours and after500 hours. The results thereof are shown in Table 1.

Example 6

For a substrate same as that in Example 5, the S-TIH1 substratemanufactured by OHARA INC. (refractive index n=1.71) was used as a glasssubstrate for coating, the SiO₂—TiO₂ coating solution used in Example 2was coated, and then a transparent amorphous SiO₂/TiO₂ film was formed.The thickness and the refractive index of the obtained film weremeasured, and the result of the measurement showed that the thicknesswas 28 nm and the refractive index was n=1.67.

Then, the glass substrate was immersed in the Al₂O₃/ZnO used in Example4, and then a coating film was formed on the surface of the glasssubstrate at a lifting speed of 1 mm/second. The glass substrate wasdried, and then thermally treated by baking at 400° C. for an hour, anda transparent amorphous Al₂O₃/ZnO film was coated thereon. The glasssubstrate was further immersed in the Al₂O₃ coating solution used inExample 1, and then a coating film was formed at a lifting speed of 1mm/second. The glass substrate was dried, and then thermally treated bybaking at 400° C. for an hour, and a transparent amorphous Al₂O₃ filmwas coated thereon. Then, the glass substrate was immersed in hot waterat 100° C. for 30 minutes, and then dried at 100° C. for 10 minutes.

The surface of the obtained film was observed by the FE-SEM to find astructure of fine irregularities in which plate crystals containingAl₂O₃ as a main component were tangled at random and complicatedly as inExample 1. For observation of the cross-section by the FE-SEM, astructure almost same as that in Example 1 was observed. The result ofmeasurement by the SPM showed that the average surface roughness Ra′value (nm) was Ra′=23 nm and the surface area ratio S_(r) was S_(r)=1.7.

Then, for the obtained film, the film thickness and the refractive indexwere measured using ellipsometry. The thickness and the refractive indexof each film are shown in Table 1.

For this substrate, a high-temperature and high-humidity test at atemperature of 60° C. and a humidity of 90% was conducted, and thetransmittance was measured at a start time, after 250 hours and after500 hours. The results thereof are shown in Table 1.

Example 7

On the clear float glass substrate used in Example 1, a SiO₂ film wasformed in a thickness of 30 nm using a magnetron sputtering apparatus.The refractive index of the film was 1.45. Then, the glass substrate wasimmersed in the Al₂O₃ coating solution used in Example 1, and then acoating film was formed at a lifting speed of 2 mm/second. The glasssubstrate was dried, and then thermally treated by baking at 400° C. foran hour, and a transparent amorphous Al₂O₃ film was coated thereon.Then, the glass substrate was immersed in hot water at 100° C. for 30minutes, and then dried at 100° C. for 10 minutes.

The surface of the obtained film was observed by the FE-SEM to find astructure of fine irregularities in which plate crystals containingAl₂O₃ as a main component were tangled at random and in a complicatedmanner as in Example 1. For observation of the cross-section by theFE-SEM, a structure almost same as that in Example 1 was observed. Theresult of measurement by the SPM showed that the average surfaceroughness Ra′ value (nm) was Ra′=22 nm and the surface area ratio S_(r)was S_(r)=1.6.

Then, for the obtained film, the film thickness and the refractive indexwere measured using ellipsometry. The thickness and the refractive indexof each film are shown in Table 1.

For this substrate, a high-temperature and high-humidity test at atemperature of 60° C. and a humidity of 90% was conducted, and thetransmittance was measured at a start time, after 250 hours and after500 hours. The results thereof are shown in Table 1.

Example 8

On the clear float glass substrate used in Example 1, a SiO₂ film wasformed in a thickness of 30 nm using a magnetron sputtering apparatus.The refractive index of the film was 1.45. Then, an Al metal film wascoated in a thickness of 35 nm by magnetron sputtering. Then, the glasssubstrate was immersed in hot water at 100° C. for 30 minutes. Ametallic luster of Al disappeared within several minutes afterimmersion, and a transparent film was left on the surface layer afterlifting. Thereafter, the glass substrate was dried at 100° C. for 10minutes.

The surface of the obtained film was observed by the FE-SEM to find astructure of fine irregularities in which plate crystals containingAl₂O₃ as a main component were tangled at random and in a complicatedmanner as in Example 1. For observation of the cross-section by theFE-SEM, a structure almost same as that in Example 1 was observed. Theresult of measurement by the SPM showed that the average surfaceroughness Ra′ value (nm) was Ra′=57 nm and the surface area ratio Sr wasSr=2.6.

Then, for the obtained film, the film thickness and the refractive indexwere measured using ellipsometry. The thickness and the refractive indexof each film are shown in Table 1.

For this substrate, a high-temperature and high-humidity test at atemperature of 60° C. and a humidity of 90% was conducted, and thetransmittance was measured at a start time, after 250 hours and after500 hours. The results thereof are shown in Table 1.

Example 9

On the TIH53 substrate used in Example 2, a composite transparent oxidefilm in which a composition ratio of SiO₂ to ZrO₂ was 7:3 was formed ina thickness of 40 nm using a dual magnetron sputtering apparatus. Therefractive index of the film was 1.65. Then, a film having Al₂O₃ and ZnOin a composition ratio of 8:2 was formed in a thickness of 50 nm by dualsputtering. An Al metal film was coated in a thickness of 25 nm bymagnetron sputtering. Then, the glass substrate was immersed in hotwater at 100° C. for 30 minutes. A metallic luster of Al disappearedwithin several minutes after immersion, and a transparent film was lefton the surface layer after lifting. Thereafter, the glass substrate wasdried at 100° C. for 10 minutes.

The surface of the obtained film was observed by the FE-SEM to find astructure of fine irregularities in which plate crystals containingAl₂O₃ as a main component were tangled at random and in a complicatedmanner as in Example 1. For observation of the cross-section by theFE-SEM, a structure almost same as that in Example 1 was observed. Theresult of measurement by the SPM showed that the average surfaceroughness Ra′ value (nm) was Ra′=42 nm and the surface area ratio S_(r)was S_(r)=2.2.

Then, for the obtained film, the film thickness and the refractive indexwere measured using ellipsometry. The thickness and the refractive indexof each film are shown in Table 1.

For this substrate, a high-temperature and high-humidity test at atemperature of 60° C. and a humidity of 90% was conducted, and thetransmittance was measured at a start time, after 250 hours and after500 hours. The results thereof are shown in Table 1.

Example 10

On the TIH01 substrate used in Example 5, a composite transparent oxidefilm in which a composition ratio of SiO₂ to ZrO₂ was 8:2 was formed ina thickness of 40 nm using a dual magnetron sputtering apparatus. Therefractive index of the film was 1.61. Then, a film having Al₂O₃ and ZnOin a composition ratio of 9:1 was formed in a thickness of 50 nm by dualsputtering. An Al metal film was coated in a thickness of 200 nm bymagnetron sputtering. Then, the glass substrate was immersed in hotwater at 100° C. for 30 minutes. A metallic luster of Al disappearedwithin several minutes after immersion, and a transparent film was lefton the surface layer after lifting. Thereafter, the glass substrate wasdried at 100° C. for 10 minutes.

The surface of the obtained film was observed by the FE-SEM to find astructure of fine irregularities in which plate crystals containingAl₂O₃ as a main component were tangled at random and complicatedly as inExample 1. For observation of the cross-section by the FE-SEM, astructure almost same as that in Example 1 was observed. The result ofmeasurement by the SPM showed that the average surface roughness Ra′value (nm) was Ra′=45 nm and the surface area ratio S_(r) was S_(r)=2.3.

Then, for the obtained film, the film thickness and the refractive indexwere measured using ellipsometry. The thickness and the refractive indexof each film are shown in Table 1.

For this substrate, a high-temperature and high-humidity test at atemperature of 60° C. and a humidity of 90% was conducted, and thetransmittance was measured at a start time, after 250 hours and after500 hours. The results thereof are shown in Table 1.

Comparative Example 1

The clear float glass substrate used in Example 1 was immersed in theAl₂O₃ sol solution used in Example 1, and then a coating film was formedon the surface of the glass substrate by the dipping method (at alifting speed of 2 mm/second, and at 20° C. and 56% R.H.). The glasssubstrate was dried, and then baked at 400° C. for an hour, and atransparent amorphous Al₂O₃ film was coated thereon. Then, the glasssubstrate was immersed in hot water at 100° C. for 30 minutes, and thendried at 100° C. for 10 minutes.

The surface of the obtained film was observed by the FE-SEM to find astructure of fine irregularities in which plate crystals containingAl₂O₃ as a main component were tangled at random and in a complicatedmanner as in Example 1. The result of measurement by the SPM showed thatthe average surface roughness Ra′ value (nm) was Ra′=28 nm and thesurface area ratio Sr was Sr=1.9.

Then, for the obtained film, the film thickness and the refractive indexwere measured using ellipsometry. The thickness and the refractive indexof each film are shown in Table 1.

For this substrate, a high-temperature and high-humidity test at atemperature of 60° C. and a humidity of 90% was conducted, and thetransmittance was measured at a start time, after 250 hours and after500 hours. The results thereof are shown in Table 1.

Comparative Example 2

The S-TIH53 substrate (refractive index n=1.84) used in Example 2 wasimmersed in the Al₂O₃/TiO₂ sol solution used in Example 3, and then acoating film was formed on the surface of the glass substrate by thedipping method (at a lifting speed of 1 mm/second, and at 20° C. and 56%R.H.). The glass substrate was dried, and then baked at 400° C. for anhour, and a transparent amorphous Al₂O₃/TiO₂ film was coated thereon.Then, the glass substrate was immersed in hot water at 100° C. for 30minutes, and then dried at 100° C. for 10 minutes.

The surface of the obtained film was observed by the FE-SEM to find astructure of fine irregularities in which plate crystals containingAl₂O₃ as a main component were tangled at random and in a complicatedmanner as in Example 1. The result of measurement by the SPM showed thatthe average surface roughness Ra′ value (nm) was Ra′=18 nm and thesurface area ratio Sr was Sr=1.5.

Then, for the obtained film, the film thickness and the refractive indexwere measured using ellipsometry. The thickness and the refractive indexof each film are shown in Table 1.

For this substrate, a high-temperature and high-humidity test at atemperature of 60° C. and a humidity of 90% was conducted, and thetransmittance was measured at a start time, after 250 hours and after500 hours. The results thereof are shown in Table 1.

Comparative Example 3

The clear float glass substrate (composition: soda lime silicate type,refractive index n=1.52) used in Example 1 was ultrasonically washedwith isopropyl alcohol, dried, and then used as a glass substrate forcoating.

A TiO₂ sol solution was added to the aforementioned SiO₂ sol solution sothat a molar ratio of SiO₂:TiO₂=3:7 was obtained, and the resultantmixture was stirred at room temperature for 2 hours, and then used as aSiO₂—TiO₂ coating solution as in Example 1. Then, the aforementionedcoating glass substrate was immersed in this coating solution, a coatingfilm was formed on the surface of the glass substrate by the dippingmethod (at a lifting speed of 0.5 mm/second, and at 20° C. and 56%R.H.). The glass substrate was dried, and then thermally treated bybaking at 400° C. for an hour, and a transparent amorphous SiO₂/TiO₂film was coated thereon.

The thickness and the refractive index of the obtained film weremeasured, and the result of the measurement showed that the thicknesswas 28 nm and the refractive index n_(s) was 2.05.

Then, the glass substrate was immersed in the Al₂O₃ sol solution used inExample 1, and then a coating film was formed on the surface of theglass substrate by the dipping method (at a lifting speed of 2mm/second, and at 20° C. and 56% R.H.). The glass substrate was dried,and then baked at 400° C. for an hour, and a transparent amorphous Al₂O₃film was coated thereon. Then, the glass substrate was immersed in hotwater at 100° C. for 30 minutes, and then dried at 100° C. for 10minutes.

The surface of the obtained film was observed by the FE-SEM to find astructure of fine irregularities in which plate crystals containingAl₂O₃ as a main component were tangled at random and in a complicatedmanner as in Example 1. The result of measurement by the SPM showed thatthe average surface roughness Ra′ value (nm) was Ra′=28 nm and thesurface area ratio Sr was Sr=1.9.

Then, for the obtained film, the film thickness and the refractive indexwere measured using ellipsometry. The thickness and the refractive indexof each film are shown in Table 1.

For this substrate, a high-temperature and high-humidity test at atemperature of 60° C. and a humidity of 90% was conducted, and thetransmittance was measured at a start time, after 250 hours and after500 hours. The results thereof are shown in Table 1.

Comparative Example 4

On the clear float glass substrate used in Example 1, an Al metal filmwas coated in a thickness of 25 nm by magnetron sputtering. Then, theglass substrate was immersed in hot water at 100° C. for 30 minutes. Ametal luster of Al disappeared within several minutes after immersion,and a transparent film was left on the surface layer after lifting.Thereafter, the glass substrate was dried at 100° C. for 10 minutes.

The surface of the obtained film was observed by the FE-SEM to find astructure of fine irregularities in which plate crystals containingAl₂O₃ as a main component were tangled at random and in a complicatedmanner as in Example 1. For observation of the cross-section by theFE-SEM, a structure almost same as that in Example 1 was observed. Theresult of measurement by the SPM showed that the average surfaceroughness Ra′ value (rim) was Ra′=32 nm and the surface area ratio S_(r)was S_(r)=2.1.

Then, for the obtained film, the film thickness and the refractive indexwere measured using ellipsometry. The thickness and the refractive indexof each film are shown in Table 1.

For this substrate, a high-temperature and high-humidity test at atemperature of 60° C. and a humidity of 90% was conducted, and thetransmittance was measured at a start time, after 250 hours and after500 hours. The results thereof are shown in Table 1.

[Table 1]

TABLE 1 Results of measurements Results ellipsometry measurements oftransmittance Film containing SiO₂ Film containing Al₂O₃ Crystal layerof plate (550 nm) Base as a main component as a main component crystalscontaining Al₂O₃ High-temperature and Refractive Refractive Refractiveas a main component high-humidity test index Thickness index Thicknessindex Thickness Refractive Start 250 500 n_(b) (nm) n_(a) (nm) n_(a)(nm) index time hours hours Example 1 1.52 20 1.48 100 1.42 230 1.42-1.099.6 99.6 99.5 Example 2 1.84 28 1.67 100 1.42 220 1.42-1.0 99.3 99.299.2 Example 3 1.84 28 1.67 30 1.60 180 1.42-1.0 99.2 99.2 99.1 Example4 1.84 28 1.67 80 1.55 300 1.53-1.0 99.5 99.5 99.3 Example 5 1.71 251.62 80 1.50 300 1.49-1.0 99.4 99.4 99.4 Example 6 1.71 28 1.67 90 1.58200 1.42-1.0 99.6 99.6 99.5 Example 7 1.52 30 1.45 100 1.42 250 1.42-1.099.3 99.3 99.3 Example 8 1.52 30 1.45 30 1.42 500 1.42-1.0 99.8 99.899.6 Example 9 1.84 40 1.65 40 1.58 400 1.54-1.0 99.4 99.3 99.3 Example10 1.71 40 1.6 30 1.54 420 1.51-1.0 99.5 99.5 99.4 Comparative 1.52 — —100 1.42 230 1.42-1.0 99.4 98.0 93.5 Example 1 Comparative 1.84 — — 301.60 180 1.42-10 97.2 93.8 89.6 Example 2 Comparative 1.52 28 2.05 1001.42 230 1.42-1.0 93.8 92.1 87.8 Example 3 Comparative 1.52 — — 30 1.42380 1.42-10 99.6 95.0 91.6 Example 4

(Note) The refractive index of the crystal layer of plate crystals showsvalues of a starting point and an ending point of a gradient refractiveindex part. For example, the refractive index 1.42-1.0 in Example 1shows that the refractive index continuously decreases from 1.42 to 1.0over a thickness of 230 nm.

[Evaluation of Performance]

If comparing transmittances at 550 nm for the fabricated transparentmembers, initial performances in Examples 1, 7 and 8, and ComparativeExamples 1 and 4 are almost same and show high values. However, for theaccelerated durability test at a high-temperature and high humidity,Examples 1, 7 and 8 having a layer containing SiO₂ as a main componentshow constant high values, whereas in Comparative Examples 1 and 4having no such a layer, the performance is considerably degraded withelapse of time. Furthermore, for a base having a high refractive index,Examples 2, 3, 4, 5, 6, 9 and 10 show a high transmittance at an initialstage and after the accelerated durability test, whereas in ComparativeExample 2 which does not have a layer containing SiO₂ as a maincomponent and Comparative Example 3 which has, in a lower layer, a layercontaining TiO₂ as a main component rather than a layer containing SiO₂as a main component and in which the relation of n_(b)≧n_(s)≧n_(a) isnot met, the transmittance is low from an initial stage and theperformance is considerably degraded as the accelerated test progresses.

Example 11

FIG. 4 is a front view of an optical member of Example 11. In thisfigure, an optical member 1 is a concave lens, and a substrate 2 isprovided with an optical transparent member 3.

FIG. 5 shows a cross-section of the optical member of Example 11 cutalong the 5-5 section in FIG. 4. A layer containing SiO₂ as a maincomponent, a layer containing Al₂O₃ as a main component, and a layerhaving arranged plate crystals containing Al₂O₃ as a main component areformed on an optical surface, and the optical transparent member 3having a shape of irregularities is formed on the outermost surface,whereby reflection of light at the optical surface is reduced.

In this example, the optical member is a concave lens, but the presentinvention is not limited thereto, and the lens may be either a convexlens or a meniscus lens.

Example 12

FIG. 6 is a front view of an optical member of Example 12. In thisfigure, an optical member 1 is a prism, and a substrate 2 is providedwith an optical transparent member 3.

FIG. 7 shows a cross-section of the optical member of Example 12 cutalong the 7-7 section in FIG. 6. A layer containing SiO₂ as a maincomponent, a layer containing Al₂O₃ as a main component, and a layerhaving arranged plate crystals containing Al₂O₃ as a main component areformed on an optical surface, and the optical transparent member 3having a shape of irregularities is formed on the outermost surface,whereby reflection of light at the optical surface is reduced.

In this example, angles formed by optical surfaces of the prism are 90°and 45°, but the present invention is not limited thereto, and theoptical surfaces of the prism may form any angle.

Example 13

FIG. 8 is a front view of an optical member of Example 13 of the presentinvention. In this figure, an optical member 1 is a fly eye integrator,and a substrate 2 is provided with an optical transparent member 3.

FIG. 9 shows a cross-section of the optical member of Example 13 cutalong the 9-9 section in FIG. 8. A layer containing SiO₂ as a maincomponent, a layer containing Al₂O₃ as a main component, and a layerhaving arranged plate crystals containing Al₂O₃ as a main component areformed on an optical surface, and the optical transparent member 3having a shape of irregularities is formed on the outermost surface,whereby reflection of light at the optical surface is reduced.

Example 14

FIG. 10 is a front view of an optical member of Example 14 of thepresent invention. In this figure, an optical member 1 is an fθ lens,and a substrate 2 is provided with an optical transparent member 3.

FIG. 11 shows a cross-section of the optical member of Example 14 cutalong the 11-11 section in FIG. 10. A layer containing SiO₂ as a maincomponent, a layer containing Al₂O₃ as a main component, and a layerhaving arranged plate crystals containing Al₂O₃ as a main component areformed on an optical surface, and the optical transparent member 3having a shape of irregularities is formed on the outermost surface,whereby reflection of light at the optical surface is reduced.

Example 15

An example in which the optical member of the present invention is usedin an observation optical system is shown as Example 15 of the presentinvention. FIG. 12 shows a cross-section of one of a pair of opticalsystems of a binocular.

In this figure, reference numeral 4 denotes an objective lens, referencenumeral 5 denotes a prism (shown in an unfolded form) for inverting animage, reference numeral 6 denotes an eye lens, reference numeral 7denotes an image formation surface, and reference numeral 8 denotes apupil surface (evaluation surface). In the figure, reference numeral 3(shown with a legend) denotes an optical transparent member relating tothe present invention, wherein a layer containing SiO₂ as a maincomponent, a layer containing Al₂O₃ as a main component, and a layerhaving arranged plate crystals containing Al₂O₃ as a main component areformed. The outermost surface has a shape of irregularities, wherebyreflection of light at each optical surface is reduced. In this example,the optical transparent member 3 consisting of a structure of fineirregularities is provided neither on an optical surface 9 of theobjective lens closest to an object nor on an optical surface 10 of theeye lens closest to the evaluation surface. The reason why the opticaltransparent member 3 is not provided on these surfaces is that itsperformance will be degraded due to contact while it is used, but thepresent invention is not limited thereto, and the optical transparentmember 3 may be provided on the optical surfaces 9 and 10.

Example 16

An example in which the optical member of the present invention is usedin an imaging optical system is shown as Example 16 of the presentinvention. FIG. 13 shows a cross-section of a photographing lens(telephoto lens is shown in this figure) of a camera or the like.

In this figure, reference numeral 7 denotes a film as an image formationsurface, or a solid imaging device (photoelectric conversion element)such as a CCD or a CMOS, and reference numeral 11 denotes a stop. In thefigure, reference numeral 3 (shown with a legend) denotes an opticaltransparent member relating to the present invention, wherein a layercontaining SiO₂ as a main component, a layer containing Al₂O₃ as a maincomponent, and a layer having arranged plate crystals containing Al₂O₃as a main component are formed, and the outermost surface has a shape ofirregularities, whereby reflection of light at each optical surface isreduced. In this example, the optical transparent member 3 consisting ofa structure of fine irregularities is not provided on an optical surface9 of the objective lens closest to an object. The reason why the opticaltransparent member 3 is not provided on the surface is that itsperformance will be degraded due to contact while it is used, but thepresent invention is not limited thereto, and the optical transparentmember 3 may be provided on the optical surface 9.

Example 17

An example in which the optical member of the present invention is usedin a projection optical system (projector) is shown as Example 17 of thepresent invention. FIG. 14 shows a cross-section of a projector opticalsystem.

In this figure, reference numeral 12 denotes a light source, referencenumerals 13 a and 13 b denote fly eye integrators, reference numeral 14denotes a polarizing conversion element, reference numeral 15 denotes acondenser lens, reference numeral 16 denotes a mirror, reference numeral17 denotes a field lens, reference numerals 18 a, 18 b, 18 c and 18 ddenote prisms, reference numerals 19 a, 19 b and 19 c denote lightmodulation elements, and reference numeral 20 denotes a projection lens.In the figure, reference numeral 3 (shown with a legend) denotes anoptical transparent member relating to the present invention, wherein alayer containing SiO₂ as a main component, a layer containing Al₂O₃ as amain component, and a layer having arranged plate crystals containingAl₂O₃ as a main component are formed, and the outermost surface has ashape of irregularities, whereby reflection of light at each opticalsurface is reduced.

Since the optical transparent member 3 of this example is configured tocontain an inorganic component such as silica or alumina as a maincomponent, it has a high heat resistance, and never suffers adegradation in performance even if placed at a position 13 a so close tothe light source 12 that the optical transparent member 3 is exposed tohigh heat.

Example 18

An example in which the optical member of the present invention is usedin a scan optical system (laser beam printer) is shown as Example 18 ofthe present invention. FIG. 15 shows a cross-section of a scan opticalsystem.

In this figure, reference numeral 12 denotes a light source, referencenumeral 21 denotes a collimator lens, reference numeral 11 denotes anaperture stop, reference numeral 22 denotes a cylindrical lens,reference numeral 23 denotes a light deflector, reference numerals 24 aand 24 b denote fθ lenses, and reference numeral 7 denotes a mirrorsurface. In the figure, reference numeral 3 (shown with a legend)denotes an optical transparent member relating to the present invention,wherein a layer containing SiO₂ as a main component, a layer containingAl₂O₃ as a main component, and a layer having arranged plate crystalscontaining Al₂O₃ as a main component are formed, and the outermostsurface has a shape of irregularities, whereby reflection of light ateach optical surface is reduced to realize formation of high-qualityimages.

This application claims priority from Japanese Patent Application No.2005-043003 filed on Feb. 18, 2005, which is hereby incorporated byreference herein.

1. A method for producing an optical member, comprising: forming a layer containing silicon oxide as a main component directly on a surface of a base, thereafter, forming a layer containing aluminum oxide as a main component directly on the layer containing silicon oxide as a main component, and subjecting the layer containing aluminum oxide as a main component to treatment with hot water, to thereby form an irregularity structure on the surface.
 2. The method according to claim 1, wherein the layer containing silicon oxide as a main component contains at least one of titanium and zirconium.
 3. The method according to claim 1, wherein the layer containing silicon oxide as a main component contains silicon oxide in a molar content of 40% or more which is the largest content among contents of all components.
 4. The method according to claim 1, wherein the layer containing aluminum oxide as a main component contains aluminum oxide in a molar content of 50% or more.
 5. The method according to claim 1, wherein a refractive index n_(b) of the base, a refractive index n_(s) of the layer containing silicon oxide as a main component, and a refractive index n_(a) of the layer containing aluminum oxide as a main component satisfies a relation of n_(b)≧n_(s)≧n_(a). 